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      前端基础面试题40道(1)
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        <span class="post-comment"><i class="icon icon-comment"></i> <a href="/blog/2020/02/11/%E5%89%8D%E7%AB%AF%E5%9F%BA%E7%A1%80%E9%9D%A2%E8%AF%95%E9%A2%9840%E9%81%93(1)/#comments" class="article-comment-link">Comments</a></span>
        
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        <figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">1.下面哪一种不属于 js 的五种基本数据类型？（）</span><br><span class="line"></span><br><span class="line">A.undefined  B.string  C.null  D.Object</span><br><span class="line"></span><br><span class="line">正确答案是:D</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">2.js数组的方法中，哪些方法不能改变自身数组？（）</span><br><span class="line"></span><br><span class="line">A.pop  B.splice  C.sort  D.concat</span><br><span class="line"></span><br><span class="line">正确答案是:D</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">3.从以下字符串</span><br><span class="line">const str &#x3D; ‘qwbewrbbeqqbbbweebbbbqee’;</span><br><span class="line">中能得到结果 [“b”, “bb”, “bbb”, “bbbb”] 以下错误语句是？</span><br><span class="line"></span><br><span class="line">A.str.match(&#x2F;b &#x2F;g)  B.str.match(&#x2F;b*&#x2F;g)  C.str.match(&#x2F;b&#123;1,4&#125;&#x2F;g)  D.str.match(&#x2F;b&#123;1,5&#125;&#x2F;g)</span><br><span class="line"></span><br><span class="line">正确答案是:A</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">4.</span>执行以下程序段后，x的值是（ ）。</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> x=<span class="number">0</span>;</span><br><span class="line"><span class="keyword">switch</span>( x )</span><br><span class="line">&#123;</span><br><span class="line"><span class="keyword">case</span> <span class="number">0</span>:   x++;</span><br><span class="line"><span class="keyword">case</span> <span class="number">1</span>:   x++;</span><br><span class="line"><span class="keyword">case</span> <span class="number">2</span>:   x++;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">A<span class="number">.1</span>  B<span class="number">.2</span>  C<span class="number">.3</span>  D<span class="number">.4</span></span><br><span class="line"></span><br><span class="line">正确答案是:C</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">5.</span>下列js可以让一个input的背景颜色变成红色的是？</span><br><span class="line"></span><br><span class="line">A.inputElement.style.backgroundColor = <span class="string">&#x27;red&#x27;</span>;</span><br><span class="line">B.inputElement.backgroundColor = <span class="string">&#x27;red&#x27;</span>;</span><br><span class="line">C.inputElement.style.backgroundColor = <span class="string">&#x27;#0000&#x27;</span>;</span><br><span class="line">D.inputElement.backgroundColor = <span class="string">&#x27;#0000&#x27;</span>;</span><br><span class="line"></span><br><span class="line">正确答案是:A</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">6.关于 this 的工作原理，下面 4 种情况的描述哪一个是错误的？（）</span><br><span class="line"></span><br><span class="line">A.在全局范围内，this指向全局对象（浏览器下指window）</span><br><span class="line">B.对象函数调用时，this指向当前对象</span><br><span class="line">C.全局函数调用时，this指向全局函数</span><br><span class="line">D.使用new实例化对象时，this指向新创建的对象</span><br><span class="line"></span><br><span class="line">正确答案是:C</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">7.</span>执行下面JavaScript 代码，页面输出的内容是（ ）。</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">showInfo</span>(<span class="params"></span>) </span>&#123;</span><br><span class="line"><span class="keyword">var</span> a = <span class="string">&quot;Hello&quot;</span>;</span><br><span class="line"><span class="keyword">var</span> b = <span class="string">&quot;World&quot;</span>;</span><br><span class="line"><span class="built_in">document</span>.write(a);	</span><br><span class="line">  <span class="keyword">return</span> b;</span><br><span class="line">&#125;</span><br><span class="line"><span class="built_in">document</span>.write(showInfo());</span><br><span class="line"></span><br><span class="line">A.Hello  B.World  C.HelloHello  D.HelloWorld</span><br><span class="line"></span><br><span class="line">正确答案是:D</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">8.</span>下属片段中，el指向dom是？（）</span><br><span class="line"></span><br><span class="line"> <span class="comment">//html</span></span><br><span class="line">&lt;div id=<span class="string">&#x27;foo&#x27;</span>&gt;</span><br><span class="line">    &lt;p id=<span class="string">&#x27;foo&#x27;</span>&gt;&lt;/P&gt;</span><br><span class="line">&lt;/div&gt;</span><br><span class="line"></span><br><span class="line"><span class="comment">//javascript</span></span><br><span class="line"><span class="keyword">var</span> el = <span class="built_in">document</span>.getElementById(<span class="string">&#x27;foo&#x27;</span>);	</span><br><span class="line"></span><br><span class="line">A.&lt;div id=’foo’&gt;&lt;<span class="regexp">/div&gt;  B.&lt;p id=”foo”&gt;&lt;/</span>p&gt;  C.null  D.以上都错误</span><br><span class="line"></span><br><span class="line">正确答案是:A</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">9.在javascript里，下列选项中不属于数组方法的是（）</span><br><span class="line"></span><br><span class="line">A.sort()  B.length()  C.concat()  D.reverse()</span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">10.</span>在JavaScript 中，能正确定义数组的有（ ）。</span><br><span class="line"></span><br><span class="line"> A.var arr = [&#123;<span class="string">&quot;name&quot;</span>:<span class="string">&quot;牛奶&quot;</span>&#125;,&#123;<span class="string">&quot;name&quot;</span>:<span class="string">&quot;面包&quot;</span>&#125;]; </span><br><span class="line"> B.var arr = [&#123;<span class="string">&quot;牛奶&quot;</span>&#125;,&#123;<span class="string">&quot;面包&quot;</span>&#125;]; </span><br><span class="line"> C.var arr = <span class="keyword">new</span> <span class="built_in">Array</span>(<span class="string">&quot;牛奶&quot;</span>,<span class="string">&quot;面包&quot;</span>); </span><br><span class="line"> D.var arr = (<span class="string">&quot;牛奶&quot;</span>,<span class="string">&quot;面包&quot;</span>);</span><br><span class="line"> </span><br><span class="line"> 正确答案是:AC</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">11.</span>在JavaScript 中，产生当前日期的方法是（ ）</span><br><span class="line"></span><br><span class="line">A.Now()  B.getDate()  C.new <span class="built_in">Date</span>()  D.new Now()</span><br><span class="line"></span><br><span class="line">正确答案是:C</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">12.下面有关JavaScript 常见事件，描述错误的是（ ）。</span><br><span class="line"></span><br><span class="line">A.onmousedown：鼠标键被按下</span><br><span class="line">B.onkeypress：键盘的键被按下或按住</span><br><span class="line">C.onblur：元素获得焦点</span><br><span class="line">D.onchange：会在域的内容改变时发生</span><br><span class="line"></span><br><span class="line">正确答案是:C</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">13.</span>分析下段代码输出结果是（ ）</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> arr = [<span class="number">2</span>,<span class="number">3</span>,<span class="number">4</span>,<span class="number">5</span>,<span class="number">6</span>];</span><br><span class="line"><span class="keyword">var</span> sum =<span class="number">0</span>;</span><br><span class="line"><span class="keyword">for</span>(<span class="keyword">var</span> i=<span class="number">1</span>;i &lt; arr.length;i++) &#123;</span><br><span class="line">sum +=arr[i] &#125;</span><br><span class="line"><span class="built_in">console</span>.log(sum);</span><br><span class="line"></span><br><span class="line">A<span class="number">.20</span>  B<span class="number">.14</span>  C<span class="number">.18</span>  D<span class="number">.12</span></span><br><span class="line"></span><br><span class="line">正确答案是:C</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">14.以下关于 Array 数组对象的说法不正确的是（ ）</span><br><span class="line"></span><br><span class="line"> A.对数组里数据的排序可以用 sort 函数，如果排序效果非预期，可以给 sort 函数加一个排序函数的参数 </span><br><span class="line"> B.reverse 用于对数组数据的倒序排列 </span><br><span class="line"> C.向数组的最后位置加一个新元素，可以用 pop 方法 </span><br><span class="line"> D.unshift 方法用于向数组删除第一个元素</span><br><span class="line"> </span><br><span class="line"> 正确答案是:CD</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">15.</span>以下代码运行的结果是输出( )</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> a = b = <span class="number">10</span>;</span><br><span class="line">(<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line"><span class="keyword">var</span> a=b=<span class="number">20</span></span><br><span class="line">&#125;)();</span><br><span class="line"><span class="built_in">console</span>.log(b);</span><br><span class="line"></span><br><span class="line">A<span class="number">.10</span>  B<span class="number">.20</span>  C.报错  D.undefined</span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">16.</span>以下代码运行后的结果是输出( )</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> a=[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>];</span><br><span class="line"><span class="built_in">console</span>.log(a.join());</span><br><span class="line"></span><br><span class="line">A<span class="number">.123</span>  B<span class="number">.1</span>,<span class="number">2</span>,<span class="number">3</span>  C<span class="number">.1</span> <span class="number">2</span> <span class="number">3</span>  D.[<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>]</span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">17.在 JS 中，’1555’+3 的运行结果是( )</span><br><span class="line"></span><br><span class="line">A.1558  B.1552  C.15553  D.1553</span><br><span class="line"></span><br><span class="line">正确答案是:C</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">18.以下代码运行后弹出的结果是( )</span><br><span class="line"></span><br><span class="line">var a &#x3D; 888;</span><br><span class="line">++a;</span><br><span class="line">alert(a++);</span><br><span class="line"></span><br><span class="line">A.888  B.889  C.890  D.891</span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">19.关于变量的命名规则，下列说法正确的是（ ）</span><br><span class="line"></span><br><span class="line"> A.首字符必须是大写或小写的字母，下划线（_）或美元符（$） </span><br><span class="line"> B.首字母的字符可以是字母，数字，下划线或美元符 </span><br><span class="line"> C.变量名称不能是保留字 </span><br><span class="line"> D.可以使用驼峰命名规则 </span><br><span class="line"> E.区分大小写</span><br><span class="line"> </span><br><span class="line"> 正确答案是:ACDE</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">20.</span>下列的哪一个表达式将返回值为假（ ）</span><br><span class="line"></span><br><span class="line">A.!(<span class="number">3</span>&lt;=<span class="number">1</span>)  B.(<span class="number">4</span>&gt;=<span class="number">4</span>)&amp;&amp;(<span class="number">5</span>&lt;=<span class="number">2</span>)  C.(“a”==“a”)&amp;&amp;(“c”!=“d”)  D.(<span class="number">2</span>&lt;<span class="number">3</span>)||(<span class="number">3</span>&lt;<span class="number">2</span>)</span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">21.</span>下面代码，k的运行结果是（ ）</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> i = <span class="number">0</span>,j = <span class="number">0</span>;</span><br><span class="line"><span class="keyword">for</span>(;i&lt;<span class="number">10</span>,j&lt;<span class="number">6</span>;i++,j++)&#123;</span><br><span class="line">k = i + j;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">A<span class="number">.16</span>  B<span class="number">.10</span>  C<span class="number">.6</span>  D<span class="number">.12</span></span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">22.</span>以下代码中 y 的值为（ ）</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> x = <span class="number">1</span>; </span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params">n</span>)</span>&#123;</span><br><span class="line">    n = n+<span class="number">1</span></span><br><span class="line">  &#125;; </span><br><span class="line">y = fn(x);</span><br><span class="line"></span><br><span class="line">A<span class="number">.2</span>  B<span class="number">.1</span>  C<span class="number">.3</span>  D.undefined</span><br><span class="line"></span><br><span class="line">正确答案是:D</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">23.</span>[<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>,<span class="number">4</span>].join(‘<span class="number">0</span>’).split(’’) 的执行结果是（ ）</span><br><span class="line"></span><br><span class="line">A.<span class="string">&#x27;1,2,3,4&#x27;</span></span><br><span class="line">B.[<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>,<span class="number">4</span>]</span><br><span class="line">C.[“<span class="number">1</span>”,“<span class="number">0</span>”,“<span class="number">2</span>”,“<span class="number">0</span>”,“<span class="number">3</span>”,“<span class="number">0</span>”,“<span class="number">4</span>”]</span><br><span class="line">D.<span class="string">&#x27;1,0,2,0,3,0,4&#x27;</span></span><br><span class="line"></span><br><span class="line">正确答案是:C</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">24.</span>以下代码中 n 的值为：（ ）</span><br><span class="line"><span class="keyword">var</span> n = <span class="string">&quot;jiao yu gai bian sheng huo&quot;</span>.indexOf(<span class="string">&quot;gai&quot;</span>,<span class="number">6</span>)；</span><br><span class="line"></span><br><span class="line">A<span class="number">.8</span>  B<span class="number">.7</span>  C<span class="number">.6</span>  D.-<span class="number">1</span></span><br><span class="line"></span><br><span class="line">正确答案是:A</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">25.alert( “12”&gt;“9” ) 的运行结果正确的是（ ）</span><br><span class="line"></span><br><span class="line">A.true  B.false  C.语法错误</span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">26.下面的描述中不正确的是（ ）</span><br><span class="line"></span><br><span class="line">A.arguments 中保存了实际传入函数内的所有参数。</span><br><span class="line">B.return 只能在函数内部使用。</span><br><span class="line">C.setInterval(fn1,1000) 只会调用一次 fn1。</span><br><span class="line">D.Date 对象的 getMonth() 获取到的值比实际月份小1。</span><br><span class="line"></span><br><span class="line">正确答案是:C</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">27.</span>下面的等式成立的是（ ）</span><br><span class="line"></span><br><span class="line">A.parseInt(<span class="number">12.5</span>) == <span class="built_in">parseFloat</span>(<span class="number">12.5</span>)</span><br><span class="line">B.Number(<span class="string">&#x27;&#x27;</span>) == <span class="built_in">parseFloat</span>(<span class="string">&#x27;&#x27;</span>)</span><br><span class="line">C.isNaN(<span class="string">&#x27;abc&#x27;</span>) == <span class="literal">NaN</span></span><br><span class="line">D.typeof <span class="literal">NaN</span> === <span class="string">&#x27;number&#x27;</span></span><br><span class="line"></span><br><span class="line">正确答案是:D</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">28.下面的描述中不正确的是（ ）</span><br><span class="line"></span><br><span class="line"> A.&#39;&#x3D;&#x3D;&#39; 在比较过程中，不但会比较两边的值，还会比较两边的数据类型。 </span><br><span class="line"> B.NaN &#x3D;&#x3D; NaN 的结果是 true。 </span><br><span class="line"> C.isNaN，判断传入的参数是否为数字，为数字返回true，否则返回false </span><br><span class="line"> D.字符串的 length 只可以获取，不可以设置。</span><br><span class="line"> </span><br><span class="line"> 正确答案是:ABC</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">29.</span>以下代码运行后，arr的结果为（ ），arr2的结果为（ ）</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> arr = [<span class="number">1</span>,<span class="number">2</span>];</span><br><span class="line"><span class="keyword">var</span> arr2 = arr.concat();</span><br><span class="line">arr2.push( arr.splice(<span class="number">1</span>,<span class="number">0</span>) );</span><br><span class="line"></span><br><span class="line"> A.[<span class="number">1</span>,<span class="number">2</span>]  B.[<span class="number">1</span>,<span class="number">2</span>,[<span class="number">2</span>]]  C.[<span class="number">1</span>,<span class="number">2</span>,[]]  D.[<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>]</span><br><span class="line"> </span><br><span class="line"> 正确答案是:AC</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">30.下面关于数组的描述正确的是（ ）</span><br><span class="line"></span><br><span class="line">A . 数组的 length 既可以获取，也可以修改。</span><br><span class="line">B . 调用 pop() 方法，不会修改原数组中的值。</span><br><span class="line">C . shift() 方法的返回值是新数组的长度。</span><br><span class="line">D . 调用 concat() 方法，会修改原数组的值。</span><br><span class="line"></span><br><span class="line">正确答案是:A</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">31.</span>分析下面的代码，输出的结果是（ ）</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> arr=<span class="keyword">new</span> <span class="built_in">Array</span>(<span class="number">5</span>);</span><br><span class="line">arr[<span class="number">1</span>]=<span class="number">1</span>;</span><br><span class="line">arr[<span class="number">5</span>]=<span class="number">2</span>;</span><br><span class="line"><span class="built_in">console</span>.log(arr.length);</span><br><span class="line"></span><br><span class="line">A<span class="number">.2</span>  B<span class="number">.5</span>  C<span class="number">.6</span>  D.报错</span><br><span class="line"></span><br><span class="line">正确答案是:C</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">32.</span>在JavaScript中，下列（ ）语句能正确获取系统当前时间的小时值。</span><br><span class="line"></span><br><span class="line">A.var date=<span class="keyword">new</span> <span class="built_in">Date</span>(); <span class="keyword">var</span> hour=date.getHour();</span><br><span class="line">B.var date=<span class="keyword">new</span> <span class="built_in">Date</span>(); <span class="keyword">var</span> hour=date.gethours();</span><br><span class="line">C.var date=<span class="keyword">new</span> date(); <span class="keyword">var</span> hour=date.getHours();</span><br><span class="line">D.var date=<span class="keyword">new</span> <span class="built_in">Date</span>(); <span class="keyword">var</span> hour=date.getHours();</span><br><span class="line"></span><br><span class="line">正确答案是:D</span><br></pre></td></tr></table></figure>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">33.请选择结果为真的选项（ ）</span><br><span class="line"></span><br><span class="line">A.null &#x3D;&#x3D; undefined  B.null &#x3D;&#x3D;&#x3D; undefined  C.undefined &#x3D;&#x3D; false  D.NaN &#x3D;&#x3D; NaN</span><br><span class="line"></span><br><span class="line">正确答案是:A</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">34.</span><span class="built_in">Math</span>.ceil(-<span class="number">3.14</span>)的结果是（ ）</span><br><span class="line"></span><br><span class="line">A.-<span class="number">3.14</span>  B.-<span class="number">3</span>  C.-<span class="number">4</span>  D<span class="number">.3</span><span class="number">.14</span></span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">35.</span><span class="built_in">Math</span>.floor(-<span class="number">3.14</span>) 的结果是（ ）</span><br><span class="line"></span><br><span class="line">A.-<span class="number">3.14</span>  B.-<span class="number">3</span>  C.-<span class="number">4</span>  D<span class="number">.3</span><span class="number">.14</span></span><br><span class="line"></span><br><span class="line">正确答案是:C</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">36.</span>阅读以下代码，在页面中结果是（ ）</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> s=<span class="string">&quot;abcdefg&quot;</span>;</span><br><span class="line">alert(s.substring(<span class="number">1</span>,<span class="number">2</span>));</span><br><span class="line"></span><br><span class="line">A.a  B.b  C.bc  D.ab</span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">37.</span>以下 ECMAScript 变量命名格式正确的是（ ）</span><br><span class="line"></span><br><span class="line">A._125dollor  B.1207A  C.-dollor  D.this</span><br><span class="line"></span><br><span class="line">正确答案是:A</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">38.</span>下列哪个不是HTML DOM的event事件？</span><br><span class="line"></span><br><span class="line">A.onclick()  B.onMove()  C.onblur()  D.onfocus()</span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">39.</span>在实际使用中，下面哪一个可以很方便的获得页面中定义的HTML对象？（）</span><br><span class="line"></span><br><span class="line">A.document.GetElementsByTagName</span><br><span class="line">B.document.getElementByTagNames</span><br><span class="line">C.document.getElementsById</span><br><span class="line">D.document.getElementById</span><br><span class="line"></span><br><span class="line">正确答案是:D</span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="number">40.</span>下面有关javaScript事件的响应，描述错误的是？</span><br><span class="line"></span><br><span class="line">A.onclick 鼠标点击某个对象</span><br><span class="line">B.onfocus 元素失去焦点</span><br><span class="line">C.onload 是某个页面的css js html 文档结构和图像被完全加载</span><br><span class="line">D.onmousedown 某个鼠标按键被按下</span><br><span class="line"></span><br><span class="line">正确答案是:B</span><br></pre></td></tr></table></figure>


      
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